1. Field of the Invention
The present invention relates to a plasma display device.
2. Description of the Related Art
At present, a plasma display device having an AC discharge type plasma display panel (hereinafter referred to as PDP), as a thin display device, is known.
The PDP has a plurality of column electrodes and a plurality of row electrode pairs arranged to intersect with the column electrodes via a discharge space. A discharge gas is sealed within the discharge space. At the intersections of the row electrode pairs and the column electrodes, discharge cells, each including the discharge space, are formed which respectively emit red light, green light, and blue light when discharging.
Each of the discharge cells uses discharge phenomenon to emit light, therefore it provides only two states, i.e., a “lighting state” to emit light at a predetermined brightness and an “extinction state”. In other words, the discharge cell only expresses two gray scale levels of brightness. Thus, in order to display halftone brightness corresponding to input video signals in the discharge cells described above, gray scale driving using a subfield method is applied (for example, see Japanese Patent Kokai No. 2000-338932).
In the subfield method, a display period for one field is divided into N subfields, and each of the subfields is designed to have a period for continuously performing either light emission or black out in the discharge cell. With this arrangement, each of the discharge cells is controlled to either a light emission state or a black out state during the period assigned to each subfield in accordance with the input video signal. Consequently, various levels of halftone brightness can be displayed at 2N (N denotes the number of subfields) levels (hereinafter referred to as gray scale levels) by the combination of subfields performing light emission within one field display period.
In performing the gray scale driving based on the subfield method, a drive unit (not shown) applies various drive pulses to the PDP to cause various discharges in the discharge cells. For example, in the first subfield, the drive unit firstly applies a reset pulse to the row electrode pairs of the PDP to create a reset discharge in all the discharge cells. On this occasion, the reset discharge uniformly forms a predetermined amount of wall charge in all the discharge cells. Subsequently, the drive unit selectively creates an erase discharge in the discharge cells from one horizontal scanning line (hereinafter referred to as a display line) to another in accordance with the input video signal. On this occasion, in the discharge cell where selective erase discharge occurs, the wall charge remaining in this discharge cell disappears. On the other hand, in the discharge cell where no selective erase discharge occurs, the wall charge formed by the reset discharge remains as it is. Subsequently, the drive unit alternately and simultaneously applies sustain pulses between all the row electrode pairs by the number of sustain pulses corresponding to the first subfield. In response to such application of the sustain pulse, only the discharge cell with the remaining wall charge repeatedly performs sustain discharge only during a period corresponding to the first subfield, and maintains the light emission state due to this sustain discharge.
However, in the PDP, the amount of wall charge formed by various discharges as described above varies due to temperature variation in the panel, the variation in display brightness, aging, etc. Therefore, there is a problem that discharge intensity fluctuates, thereby deteriorating the display quality.